I wonder if something like this is a little easier to read?
(defn generate
([f coll]
(generate f coll (reverse coll)))
([f coll args]
(let [next-val (apply f args)]
(lazy-cat coll (generate f [next-val] (conj (butlast args) next-val))))))
Where your Fibonacci example becomes:
(take 100 (generate +’ [1 1]))
As for your other questions, I can’t be of much help. But isn’t there
nontrivial memory overhead to consider with this approach?
> On Sep 22, 2015, at 18:19, nchurch <[email protected]> wrote:
>
> I was going through 4clojure (highly recommended!) and doing the Fibonacci
> exercise. It occurred to me that the iterate function could be generalized
> in a reasonable way, so that the next value is generated by applying the
> function to the last N items so far, where N is the number of initial
> arguments beyond the function. Thus:
>
> (generate inc 1)
>
> works just like iterate, while
>
> (generate + 1 1)
>
> generates the Fibonacci sequence.
>
> Here's the code:
>
> (defn generate
> [f & more]
> (letfn [(recurse
> [coll args]
> (let [next-val (apply f args)]
> (lazy-cat coll (recurse [next-val] (conj (butlast args)
> next-val)))))]
> (recurse more (reverse more))))
>
> Code is also on Github <https://github.com/nchurch/generate>.
>
> I see this as part of a larger class of generalized sequence functions: for
> instance, extra arguments in a function given to reduce could refer to N
> arguments back in the sequence (might be useful, for instance, in smoothing a
> sequence of values using an average).
>
> Questions: is there an existing home for this kind of functionality? And
> could the above code be improved? (I just used the definition of iterate as
> a starting point.)
>
>
>
>
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